Indicator Species

UXL Encyclopedia of Science
COPYRIGHT 2002 The Gale Group, Inc.

Indicator species

Indicator species are plants and animals that, by their presence, abundance, or chemical composition, demonstrate some distinctive aspect of the character or quality of the environment. For example, in areas where metal-rich minerals can be found at the soil surface, indicator species of plants accumulate large concentrations of those minerals in their tissues. Studies have shown levels of nickel as high as 10 percent in the tissues of some varieties of the mustard plant in Russia and as high as 25 percent in the tissues of the Sebertia acuminata from the Pacific island of New Caledonia. Similarly, a relative of the mint plant found in parts of Africa has been important in the discovery of copper deposits. This plant grows only in areas that have up to 7 percent copper in their soil.

Ecological significance

More recently, indicator species have begun being used as measures of habitat or ecosystem quality. For example, many species of lichens are very sensitive to toxic gases, such as sulfur dioxide and ozone. These organisms have been monitored in many places to study air pollution. Severe damage to lichens is especially common in cities with chronic air pollution and near large producers of toxic gases, such as metal smelters.

Similarly, certain types of aquatic invertebrates and fish have been surveyed as indicators of water quality and the health of aquatic ecosystems. For example, the presence of "sewage worms" (tubificids) is an

almost certain indication that water quality has been degraded by sewage or other oxygen-consuming organic matter. In contrast with most of the animals that live in an unpolluted aquatic environment, tubificid worms can tolerate water almost totally lacking in oxygen.

In some cases, indicator species can be used as measures of the quality of whole habitats or ecosystems. For example, animals with a specialized requirement for old-growth forests can be used as an indicator of the health of that type of ecosystem. Old-growth dependent birds in North America include spotted owls, red-cockaded woodpeckers, and marbled murrelets. If birds such as these thrive in a particular old-growth forest, the forest can be considered to be in good ecological health. On the other hand, if the health of such species begins to decline, the indication is that the habitat itself may be in poor condition.

Many governments are currently conducting research to determine which species of animals or plants can act as sentinels or lookouts for particular environmental contaminants. Through the use of indicator species, it is hoped that potential environmental problems can be identified before they result in irreparable damage.

[See alsoPollution ]

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Indicator Species

World of Microbiology and Immunology
COPYRIGHT 2003 The Gale Group Inc.

Indicator species

Indicator organisms are used to monitor water, food or other samples for the possibility of microbial contamination . The detection of the designated species is an indication that harmful microbes, which are found in the same environment as the indicator species, may be present in the sample.

Indicator organisms serve as a beacon of fecal contamination. The most common fecal microorganism that is used have in the past been designated as fecal coliforms. Now, with more specific growth media available, testing for Escherichia coli can be done directly. The detection of Escherichia coli indicates the presence of fecal material from warm-blooded animals, and so the possible presence of disease producing bacteria , such as Salmonella, Shigella, and Vibrio.

To be an indicator organism, the bacteria must fulfill several criteria. The species should always be present in the sample whenever the bacterial pathogens are present. The indicator should always be present in greater numbers than the pathogen. This increases the chances of detecting the indicator. Testing directly for the pathogen, which can be more expensive and time-consuming, might yield a negative result if the numbers of the pathogen are low. Thirdly, the indicator bacterial species should be absent, or present in very low numbers, in clean water or other uncontaminated samples. Fourth, the indicator should not grow more abundantly than the pathogen in the same environment. Fifth, the indicator should respond to disinfection or sterilization treatments in the same manner as the pathogen does. For example, Escherichia coli responds to water disinfection treatments, such as chlorination , ozone, and ultra-violet irradiation, with the same sensitivity as does Salmonella. Thus, if the indicator organism is killed by the water treatment, the likelihood of Salmonella being killed also is high.

Another indicator bacterial species that is used are of the fecal Streptococcus group. These have been particularly useful in salt water monitoring, as they persist longer in the salt water than does Escherichia coli. In addition, the ratio of fecal coliform bacteria to fecal streptococci can provide an indication of whether the fecal contamination is from a human or another warm-blooded animal.

The use of indicator bacteria has long been of fundamental importance in the monitoring of drinking water. Similar indicator organisms will be needed to monitor water against the emerging protozoan threats of giardia and cryptosporidium .

See also Antibiotic resistance, tests for; Water quality

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indicator species

indicator species1. A species that is of narrow ecological amplitude with respect to one or more environmental factors and which is, when present, therefore indicative of a particular environmental condition or set of conditions. For example, the lichen Usnea articulata occurs only where levels of atmospheric sulphur dioxide are low and the nettle (Urtica dioica) indicates high levels of phosphate. If species are long-lived their performance represents an integration of the influence of the factor with time and may give a better assessment of its importance than can a more precise physical measurement taken on a particular day.

3. In plant community classification the term is used more loosely to denote the most characteristic community members. In this case ‘indicator species’ may include species typical of and vigorous in a particular environment and is not necessarily restricted to species of narrow ecological amplitude.

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indicator species analysis

indicator species analysis In general, a classificatory scheme in which the final groups are characterized by indicator species derived from the data in the course of group definition. More specifically, the term refers to a polythetic divisive classificatory scheme proposed by M. O. Hill in 1975. Sites are ranked by a reciprocal averaging ordination and divided into two groups at the mid-point (the ‘centre of gravity’) of all the weighted data values of the ordination. Indicator species (usually five) are then identified as those species exclusively, or most nearly, associated with one or other side of this division (positive and negative indicators). The site-indicator scores, effectively a rough secondary ordination, determine their final classification; and the process may then be repeated within the groups identified. The indicator species form a key, enabling new sites to be added easily into the classificatory framework without excessive recalculation.

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indicator species analysis

indicator species analysis In general, a classificatory scheme in which the final groups are characterized by indicator species derived from the data in the course of group definition. More specifically, the term refers to a polythetic divisive classificatory scheme proposed by M. O. Hill in 1975. Sites are ranked by a reciprocal averaging ordination and divided into 2 groups at the mid-point (the ‘centre of gravity’) of all the weighted data values of the ordination. Indicator species (usually 5) are then identified as those species exclusively, or most nearly so, associated with one or other side of this division (positive and negative indicators). The site-indicator scores, effectively a rough secondary ordination, determine their final classification; and the process may then be repeated within the groups identified. The indicator species form a key, enabling new sites to be added easily into the classificatory framework without excessive recalculation.

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indicator species

indicator species A species that is of narrow ecological amplitude with respect to one or more environmental factors and that is, when present, therefore indicative of a particular environmental condition or set of conditions. For example, fish species and many aquatic invertebrates vary in the amount of dissolved oxygen they require and the species present in a body of water provide an indication of the extent to which the water is contaminated with organic material. If species are long-lived their performance represents an integration of the influence of the factor with time and may give a better assessment of its importance than can a more precise physical measurement taken on a particular day. See also INDUSTRIAL MELANISM.

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indicator species

indicator species1. A species that is of narrow ecological amplitude with respect to one or more environmental factors and that is, when present, therefore indicative of a particular environmental condition or set of conditions. In geobotanical surveys, species or ecotypes with high heavy-metal tolerance have been used as indicators of metallic ore.

2. In plant community classification, the term is used more loosely to denote the most characteristic community members. In this case ‘indicator species’ may include species typical of and vigorous in a particular environment and is not necessarily restricted to species of narrow ecological amplitude. See also GEOBOTANICAL EXPLORATION.

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indicator species

indicator species A plant or animal species that is very sensitive to a particular environmental factor, so that its presence (or absence) in an area can provide information about the levels of that factor. For example, some lichens are very sensitive to the concentration of sulphur dioxide (a major pollutant) in the atmosphere. Examination of the lichens present in an area can provide a good indication of the prevailing levels of sulphur dioxide.

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